Accumulate intermediate expressions into `CoverageCounters`

This avoids the need to pass around a separate vector to accumulate into, and
avoids the need to create a fake empty vector when failure occurs.

3 files changed, 63 insertions, 95 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/counters.rs b/compiler/rustc_mir_transform/src/coverage/counters.rs
index 938ef4975bb..ed362a72e92 100644
--- a/compiler/rustc_mir_transform/src/coverage/counters.rs
+++ b/compiler/rustc_mir_transform/src/coverage/counters.rs
@@ -18,6 +18,12 @@ pub(super) struct CoverageCounters {
     function_source_hash: u64,
     next_counter_id: CounterId,
     next_expression_id: ExpressionId,
+
+    /// Expression nodes that are not directly associated with any particular
+    /// BCB/edge, but are needed as operands to more complex expressions.
+    /// These are always `CoverageKind::Expression`.
+    pub(super) intermediate_expressions: Vec<CoverageKind>,
+
     pub debug_counters: DebugCounters,
 }
 
@@ -27,6 +33,9 @@ impl CoverageCounters {
             function_source_hash,
             next_counter_id: CounterId::START,
             next_expression_id: ExpressionId::START,
+
+            intermediate_expressions: Vec::new(),
+
             debug_counters: DebugCounters::new(),
         }
     }
@@ -38,13 +47,13 @@ impl CoverageCounters {
     }
 
     /// Makes `CoverageKind` `Counter`s and `Expressions` for the `BasicCoverageBlock`s directly or
-    /// indirectly associated with `CoverageSpans`, and returns additional `Expression`s
+    /// indirectly associated with `CoverageSpans`, and accumulates additional `Expression`s
     /// representing intermediate values.
     pub fn make_bcb_counters(
         &mut self,
         basic_coverage_blocks: &mut CoverageGraph,
         coverage_spans: &[CoverageSpan],
-    ) -> Result<Vec<CoverageKind>, Error> {
+    ) -> Result<(), Error> {
         MakeBcbCounters::new(self, basic_coverage_blocks).make_bcb_counters(coverage_spans)
     }
 
@@ -134,13 +143,9 @@ impl<'a> MakeBcbCounters<'a> {
     /// Returns any non-code-span expressions created to represent intermediate values (such as to
     /// add two counters so the result can be subtracted from another counter), or an Error with
     /// message for subsequent debugging.
-    fn make_bcb_counters(
-        &mut self,
-        coverage_spans: &[CoverageSpan],
-    ) -> Result<Vec<CoverageKind>, Error> {
+    fn make_bcb_counters(&mut self, coverage_spans: &[CoverageSpan]) -> Result<(), Error> {
         debug!("make_bcb_counters(): adding a counter or expression to each BasicCoverageBlock");
         let num_bcbs = self.basic_coverage_blocks.num_nodes();
-        let mut collect_intermediate_expressions = Vec::with_capacity(num_bcbs);
 
         let mut bcbs_with_coverage = BitSet::new_empty(num_bcbs);
         for covspan in coverage_spans {
@@ -161,16 +166,10 @@ impl<'a> MakeBcbCounters<'a> {
         while let Some(bcb) = traversal.next(self.basic_coverage_blocks) {
             if bcbs_with_coverage.contains(bcb) {
                 debug!("{:?} has at least one `CoverageSpan`. Get or make its counter", bcb);
-                let branching_counter_operand =
-                    self.get_or_make_counter_operand(bcb, &mut collect_intermediate_expressions)?;
+                let branching_counter_operand = self.get_or_make_counter_operand(bcb)?;
 
                 if self.bcb_needs_branch_counters(bcb) {
-                    self.make_branch_counters(
-                        &mut traversal,
-                        bcb,
-                        branching_counter_operand,
-                        &mut collect_intermediate_expressions,
-                    )?;
+                    self.make_branch_counters(&mut traversal, bcb, branching_counter_operand)?;
                 }
             } else {
                 debug!(
@@ -182,7 +181,7 @@ impl<'a> MakeBcbCounters<'a> {
         }
 
         if traversal.is_complete() {
-            Ok(collect_intermediate_expressions)
+            Ok(())
         } else {
             Error::from_string(format!(
                 "`TraverseCoverageGraphWithLoops` missed some `BasicCoverageBlock`s: {:?}",
@@ -196,7 +195,6 @@ impl<'a> MakeBcbCounters<'a> {
         traversal: &mut TraverseCoverageGraphWithLoops,
         branching_bcb: BasicCoverageBlock,
         branching_counter_operand: Operand,
-        collect_intermediate_expressions: &mut Vec<CoverageKind>,
     ) -> Result<(), Error> {
         let branches = self.bcb_branches(branching_bcb);
         debug!(
@@ -232,17 +230,10 @@ impl<'a> MakeBcbCounters<'a> {
                         counter",
                         branch, branching_bcb
                     );
-                    self.get_or_make_counter_operand(
-                        branch.target_bcb,
-                        collect_intermediate_expressions,
-                    )?
+                    self.get_or_make_counter_operand(branch.target_bcb)?
                 } else {
                     debug!("  {:?} has multiple incoming edges, so adding an edge counter", branch);
-                    self.get_or_make_edge_counter_operand(
-                        branching_bcb,
-                        branch.target_bcb,
-                        collect_intermediate_expressions,
-                    )?
+                    self.get_or_make_edge_counter_operand(branching_bcb, branch.target_bcb)?
                 };
                 if let Some(sumup_counter_operand) =
                     some_sumup_counter_operand.replace(branch_counter_operand)
@@ -258,7 +249,7 @@ impl<'a> MakeBcbCounters<'a> {
                         self.format_counter(&intermediate_expression)
                     );
                     let intermediate_expression_operand = intermediate_expression.as_operand();
-                    collect_intermediate_expressions.push(intermediate_expression);
+                    self.coverage_counters.intermediate_expressions.push(intermediate_expression);
                     some_sumup_counter_operand.replace(intermediate_expression_operand);
                 }
             }
@@ -290,18 +281,13 @@ impl<'a> MakeBcbCounters<'a> {
         Ok(())
     }
 
-    fn get_or_make_counter_operand(
-        &mut self,
-        bcb: BasicCoverageBlock,
-        collect_intermediate_expressions: &mut Vec<CoverageKind>,
-    ) -> Result<Operand, Error> {
-        self.recursive_get_or_make_counter_operand(bcb, collect_intermediate_expressions, 1)
+    fn get_or_make_counter_operand(&mut self, bcb: BasicCoverageBlock) -> Result<Operand, Error> {
+        self.recursive_get_or_make_counter_operand(bcb, 1)
     }
 
     fn recursive_get_or_make_counter_operand(
         &mut self,
         bcb: BasicCoverageBlock,
-        collect_intermediate_expressions: &mut Vec<CoverageKind>,
         debug_indent_level: usize,
     ) -> Result<Operand, Error> {
         // If the BCB already has a counter, return it.
@@ -354,7 +340,6 @@ impl<'a> MakeBcbCounters<'a> {
         let first_edge_counter_operand = self.recursive_get_or_make_edge_counter_operand(
             predecessors.next().unwrap(),
             bcb,
-            collect_intermediate_expressions,
             debug_indent_level + 1,
         )?;
         let mut some_sumup_edge_counter_operand = None;
@@ -362,7 +347,6 @@ impl<'a> MakeBcbCounters<'a> {
             let edge_counter_operand = self.recursive_get_or_make_edge_counter_operand(
                 predecessor,
                 bcb,
-                collect_intermediate_expressions,
                 debug_indent_level + 1,
             )?;
             if let Some(sumup_edge_counter_operand) =
@@ -380,7 +364,7 @@ impl<'a> MakeBcbCounters<'a> {
                     self.format_counter(&intermediate_expression)
                 );
                 let intermediate_expression_operand = intermediate_expression.as_operand();
-                collect_intermediate_expressions.push(intermediate_expression);
+                self.coverage_counters.intermediate_expressions.push(intermediate_expression);
                 some_sumup_edge_counter_operand.replace(intermediate_expression_operand);
             }
         }
@@ -403,32 +387,21 @@ impl<'a> MakeBcbCounters<'a> {
         &mut self,
         from_bcb: BasicCoverageBlock,
         to_bcb: BasicCoverageBlock,
-        collect_intermediate_expressions: &mut Vec<CoverageKind>,
     ) -> Result<Operand, Error> {
-        self.recursive_get_or_make_edge_counter_operand(
-            from_bcb,
-            to_bcb,
-            collect_intermediate_expressions,
-            1,
-        )
+        self.recursive_get_or_make_edge_counter_operand(from_bcb, to_bcb, 1)
     }
 
     fn recursive_get_or_make_edge_counter_operand(
         &mut self,
         from_bcb: BasicCoverageBlock,
         to_bcb: BasicCoverageBlock,
-        collect_intermediate_expressions: &mut Vec<CoverageKind>,
         debug_indent_level: usize,
     ) -> Result<Operand, Error> {
         // If the source BCB has only one successor (assumed to be the given target), an edge
         // counter is unnecessary. Just get or make a counter for the source BCB.
         let successors = self.bcb_successors(from_bcb).iter();
         if successors.len() == 1 {
-            return self.recursive_get_or_make_counter_operand(
-                from_bcb,
-                collect_intermediate_expressions,
-                debug_indent_level + 1,
-            );
+            return self.recursive_get_or_make_counter_operand(from_bcb, debug_indent_level + 1);
         }
 
         // If the edge already has a counter, return it.
diff --git a/compiler/rustc_mir_transform/src/coverage/mod.rs b/compiler/rustc_mir_transform/src/coverage/mod.rs
index f713613d313..750e2a2a215 100644
--- a/compiler/rustc_mir_transform/src/coverage/mod.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mod.rs
@@ -199,52 +199,47 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
         // `BasicCoverageBlock`s not already associated with a `CoverageSpan`.
         //
         // Intermediate expressions (used to compute other `Expression` values), which have no
-        // direct associate to any `BasicCoverageBlock`, are returned in the method `Result`.
-        let intermediate_expressions_or_error = self
+        // direct association with any `BasicCoverageBlock`, are accumulated inside `coverage_counters`.
+        let result = self
             .coverage_counters
             .make_bcb_counters(&mut self.basic_coverage_blocks, &coverage_spans);
 
-        let (result, intermediate_expressions) = match intermediate_expressions_or_error {
-            Ok(intermediate_expressions) => {
-                // If debugging, add any intermediate expressions (which are not associated with any
-                // BCB) to the `debug_used_expressions` map.
-                if debug_used_expressions.is_enabled() {
-                    for intermediate_expression in &intermediate_expressions {
-                        debug_used_expressions.add_expression_operands(intermediate_expression);
-                    }
+        if let Ok(()) = result {
+            // If debugging, add any intermediate expressions (which are not associated with any
+            // BCB) to the `debug_used_expressions` map.
+            if debug_used_expressions.is_enabled() {
+                for intermediate_expression in &self.coverage_counters.intermediate_expressions {
+                    debug_used_expressions.add_expression_operands(intermediate_expression);
                 }
-
-                ////////////////////////////////////////////////////
-                // Remove the counter or edge counter from of each `CoverageSpan`s associated
-                // `BasicCoverageBlock`, and inject a `Coverage` statement into the MIR.
-                //
-                // `Coverage` statements injected from `CoverageSpan`s will include the code regions
-                // (source code start and end positions) to be counted by the associated counter.
-                //
-                // These `CoverageSpan`-associated counters are removed from their associated
-                // `BasicCoverageBlock`s so that the only remaining counters in the `CoverageGraph`
-                // are indirect counters (to be injected next, without associated code regions).
-                self.inject_coverage_span_counters(
-                    coverage_spans,
-                    &mut graphviz_data,
-                    &mut debug_used_expressions,
-                );
-
-                ////////////////////////////////////////////////////
-                // For any remaining `BasicCoverageBlock` counters (that were not associated with
-                // any `CoverageSpan`), inject `Coverage` statements (_without_ code region `Span`s)
-                // to ensure `BasicCoverageBlock` counters that other `Expression`s may depend on
-                // are in fact counted, even though they don't directly contribute to counting
-                // their own independent code region's coverage.
-                self.inject_indirect_counters(&mut graphviz_data, &mut debug_used_expressions);
-
-                // Intermediate expressions will be injected as the final step, after generating
-                // debug output, if any.
-                ////////////////////////////////////////////////////
-
-                (Ok(()), intermediate_expressions)
             }
-            Err(e) => (Err(e), Vec::new()),
+
+            ////////////////////////////////////////////////////
+            // Remove the counter or edge counter from of each `CoverageSpan`s associated
+            // `BasicCoverageBlock`, and inject a `Coverage` statement into the MIR.
+            //
+            // `Coverage` statements injected from `CoverageSpan`s will include the code regions
+            // (source code start and end positions) to be counted by the associated counter.
+            //
+            // These `CoverageSpan`-associated counters are removed from their associated
+            // `BasicCoverageBlock`s so that the only remaining counters in the `CoverageGraph`
+            // are indirect counters (to be injected next, without associated code regions).
+            self.inject_coverage_span_counters(
+                coverage_spans,
+                &mut graphviz_data,
+                &mut debug_used_expressions,
+            );
+
+            ////////////////////////////////////////////////////
+            // For any remaining `BasicCoverageBlock` counters (that were not associated with
+            // any `CoverageSpan`), inject `Coverage` statements (_without_ code region `Span`s)
+            // to ensure `BasicCoverageBlock` counters that other `Expression`s may depend on
+            // are in fact counted, even though they don't directly contribute to counting
+            // their own independent code region's coverage.
+            self.inject_indirect_counters(&mut graphviz_data, &mut debug_used_expressions);
+
+            // Intermediate expressions will be injected as the final step, after generating
+            // debug output, if any.
+            ////////////////////////////////////////////////////
         };
 
         if graphviz_data.is_enabled() {
@@ -257,7 +252,7 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
                 &self.basic_coverage_blocks,
                 &self.coverage_counters.debug_counters,
                 &graphviz_data,
-                &intermediate_expressions,
+                &self.coverage_counters.intermediate_expressions,
                 &debug_used_expressions,
             );
         }
@@ -273,7 +268,7 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
 
         ////////////////////////////////////////////////////
         // Finally, inject the intermediate expressions collected along the way.
-        for intermediate_expression in intermediate_expressions {
+        for intermediate_expression in self.coverage_counters.intermediate_expressions.drain(..) {
             inject_intermediate_expression(self.mir_body, intermediate_expression);
         }
     }
diff --git a/compiler/rustc_mir_transform/src/coverage/tests.rs b/compiler/rustc_mir_transform/src/coverage/tests.rs
index 248a192f8f5..0699723fdc4 100644
--- a/compiler/rustc_mir_transform/src/coverage/tests.rs
+++ b/compiler/rustc_mir_transform/src/coverage/tests.rs
@@ -676,10 +676,10 @@ fn test_make_bcb_counters() {
             }
         }
         let mut coverage_counters = counters::CoverageCounters::new(0);
-        let intermediate_expressions = coverage_counters
+        let () = coverage_counters
             .make_bcb_counters(&mut basic_coverage_blocks, &coverage_spans)
             .expect("should be Ok");
-        assert_eq!(intermediate_expressions.len(), 0);
+        assert_eq!(coverage_counters.intermediate_expressions.len(), 0);
 
         let_bcb!(1);
         assert_eq!(